In the field of graphic art, an image is printed on a printing plate using a set of color-separation films prepared from a color original by using lithographic films. In general, a color proof is manufactured from the color-separation films before the main printing (i.e., actual printing operation) so as to check for errors in the color separation process or whether color correction or the like is necessary. The color proof is required to realize high resolution for enabling the formation of a halftone image with high reproducibility and to have capabilities such as high process stability. Furthermore, in order to obtain a color proof approximated to an actual printed matter, the materials used for the actual printed matter are preferably used for the materials of the color proof, for example, the substrate is preferably printing paper and the coloring material is preferably a pigment. With respect to the method for manufacturing the color proof, a dry process of using no developer solution is highly demanded.
Accompanying recent widespread use of computerized systems in the pre-printing process (in the pre-press field), a recording system of producing a color proof directly from digital signals has been developed as the dry preparation method of a color proof. These computerized systems are configured particularly for the purpose of producing a color proof having high image quality and by these systems, a halftone image of 150 lines/inch or more is generally produced. In order to record a proof having high image quality from digital signals, laser light capable of modulating by the digital signals and sharply focusing the recording light is used as the recording head. Accordingly, the recording material used with the laser is required to exhibit high recording sensitivity to the laser light and high resolution for enabling the reproduction of high definition halftone dots.
With respect to the recording material for use in the transfer image formation method utilizing laser light, a heat-fusion transfer sheet is known, where a light-to-heat conversion layer capable of generating heat upon absorption of laser light and an image-forming layer containing a pigment dispersed in a heat-fusible component such as wax or binder are provided on a support in this order (see, JP-A-5-58045 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)). According to the image formation method using this recording material, heat is generated in the region irradiated with laser light of the light-to-heat conversion layer and the image-forming layer corresponding to the region is fused by the heat and transferred to an image-receiving sheet stacked and disposed on the transfer sheet, whereby a transfer image is formed on the image-receiving sheet.
JP-A-6-219052 discloses a thermal transfer sheet where a light-to-heat conversion layer containing a light-to-heat converting substance, a very thin (0.03 to 0.3 μm) thermal release layer and an image-forming layer containing a coloring material are provided in this order on a support. In this thermal transfer sheet, upon irradiation with laser light, the bonding strength between the image-forming layer and the light-to-heat conversion layer bonded with an intervention of the thermal release layer is weakened and a high definition image is formed on an image-receiving sheet stacked and disposed on the thermal transfer sheet. This image formation method utilizes so-called “ablation”, more specifically, a phenomenon that a part of the thermal release layer in the region irradiated with laser light is decomposed and vaporized and thereby the bonding strength between the image-forming layer and the light-to-heat conversion layer is weakened in that region, as a result, the image-forming layer in that region is transferred to an image-receiving sheet stacked on the thermal transfer sheet.
These image formation methods are advantageous in that a printing paper having provided thereon an image-receiving layer (adhesive layer) can be used as the image-receiving sheet material and a multicolor image can be easily obtained by sequentially transferring images of different colors on the image-receiving sheet. In particular, the image formation method using ablation is advantageous in that a high definition image can be easily obtained. Therefore, this method is useful for the production of a color proof (DDCP (direct digital color proof)) or a high definition mask image.
In a multicolor image-forming material for use in such a multicolor image formation method, the light-to-heat conversion layer or image-forming layer of the thermal transfer sheet is formed by a coating method. The image-receiving layer of the image-receiving sheet is also formed by a coating method. In order to obtain stable transfer, the image-forming layer of the thermal transfer sheet must be uniformly coated. If the image-forming layer is not uniformly coated, an uneven surface results or unevenness is generated in the surface energy or adhesive strength and this adversely affects the transfer to the image-receiving sheet. For the purpose of improving the uniformity of the coated surface, a fluorine-containing surfactant is used in some cases, however, this often causes bubbling of the coating solution to impair the in-plane uniformity and give a non-uniform concentration. The image-receiving layer of the page-receiving sheet must be also uniformly coated so that the image formed on the image-forming layer of the thermal transfer sheet can be evenly and stably transferred. If the image-receiving layer is not uniformly coated, an uneven surface results or unevenness is generated in the surface energy or adhesive strength and this impairs uniform transfer to the image-receiving sheet.